This invention relates generally to sonobuoys and more particularly to the deployment of sonobuoys through an ice layer.
The Artic ice pack presents a formidable barrier to anti-submarine warefare systems. A sonobuoy system deployed under the ice could provide a capability for monitoring submarine movements. Existing sonobuoy systems are generally not sufficiently rugged to provide penetration capability in an ice mass of unknown thickness and yet still protect internal equipment from the forces encountered during ice penetration and water entry.
An existing, experimental probe system disclosed in U.S. patent application, Ser. No. 441,202 filed by Feltz et al on Feb. 5, 1974 consists of a penetrator to perforate the ice, an afterbody to house the sonobuoy electronics, hydrophone and cable, and an antenna section. Each of the three parts separate during ice penetration, with the afterbody remaining interconnected to the antenna section by an umbilical line of coaxial cable. The afterbody and antenna sections are buoyant, and the antenna remains at the ice surface after penetration. A hydrophone is then released at this time and suspended from the afterbody. The afterbody may remain embedded in the ice layer if the layer is of considerable thickness, or it may penetrate a thin layer of ice and remain afloat beneath the ice.
This system has several disadvantages. The afterbody must be of a certain density or buoyancy to work properly and also be of a certain size and shape to have the proper coefficient of drag in the water if it penetrates through a thin ice layer. The probe must have a certain weight per area ratio and have a high percentage of the system weight in order to achieve successful penetration of the ice layer. These requirements on the probe mean that with a small increase in the weight of the components carried within the afterbody, a dynamic imbalance would be created on the overall system, resulting in the limitation that only very small electronic, acoustic and power generating components could be carried within and be deployed from the afterbody.
Since the antenna section and the afterbody section are decelerated completely at or shortly after ice impact, and since most of the sensitive electronics equipment is within the after-body, this equipment is subjected to extreme shock loads which may seriously affect the reliable operation of the system.
Another significant problem with this experimental system is that the hole bored through the ice does not always remain clear to permit a hydrophone to be dropped into the water below the ice. The afterbody would plug the top of the hole and trap air in the cavity made by the probe, allowing water to flow a few inches up into the hole, compressing the air. The water in the hole contains crushed ice or slush that sometimes prevents the hydrophone and/or other components from falling into the seawater. The hydrophone is released from the afterbody after the sonobuoy system has come to rest, with the hydrophone release being delayed to avoid the difficult problem of designing a system that would be capable of deploying the hydrophone from the probe during ice penetration at a high speed and still bring the hydrophone safely to rest at the desired depth. Further, the compressed air entrapped within the hole precludes the use of sea water-activated batteries since seawater cannot reach the battery located in the after-body.